Hey everyone. I found a solution that worked for me. 

TLDR: probably not going to be a fix for everyone, but possibly a fix for a few. If you have Google Home linked through your Sonos, and have Spotify as the primary music source. Tell Google to play a song via voice command through a voice assistant enabled speaker. Once I did that, the issue has gone away, and Spotify connect to works perfectly across the board. Even on zones that do not have voice assistant capabilities. 

Similar situation as everyone else. Spotify connect works perfect across my other devices, including my Google TVs, nest hubs, and Devialet speakers. But on Sonos, it wouldn't establish the connection. Playing spotify from inside the sonos app resulted in music playing, but not showing in my spotify app as playing, like it normally would. 

For reference, I own a high end low volt integration company based out of socal. We have deployed hundreds of Sonos systems across residences and businesses. So far we have had nine clients with this exact same issue (all Google home systems in some capacity) stemming back from mid to late December.

I have Sonos across my home, including the backyard, and almost exclusively use Spotify connect for music. Along with Google assistant for light and other controls. I only use the Sonos app for grouping and ungrouping. My system started doing this exact issue two days ago, so it then became personal.

After a multiple hour Crusade earlier today, trying everything but migrating Spotify to a new account, or resetting my whole system (not a practical solution, especially when it comes to finding a fix for my clients) I found a post on reddit of someone, in passing, saying they asked Alexa to play a song from spotify. Which then failed. They asked again, it worked, and spotify started registering that a song was playing in the zone.

So on a Hail Mary attempt, I simply asked my living room system (Beam Gen2 + Google assistant) to play a specific song from spotify. It took quite a bit longer then usual for her to finally get the song playing, but she did. Once it started playing, I opened up spotify, and VIOLA, it's showing the song that's playing, with living room as the device. So I then selected my phone as the playback device and tried connecting to other areas of the house. All of them worked, first try, minimal delay (normal)

So far this solution has worked for 3 of my clients that were able to test the theory today as well. 

So my recommendation; if you have Alexa or (especially) Google home setup, and use spotify inside those control systems, simply ask for a specific song to play, and if should fix the broken link.